With the purpose in searching green energy resources, SOFC has become alternative choice since it is practicable in variety of fuels and low emission. The state-of-the-art oxide ion conducting electrolyte for SOFC is yttria-stabilized zirconia (YSZ) which operates at high temperature (800° C.-1000° C.). Due to some disadvantages of high temperature operation, intermediate temperature solid oxide fuel cells (IT-SOFCs) are becoming more and more attractive.
Proton conducting generally electrolytes operates at 400-700° C. In this intermediate temperature range, several perovskite electrolytes i.e. ABO3 exhibit good electrochemical properties in term of proton conductivity. Although using oxide ion conductor in SOFC is typical, the troubles are still presence in terms of mismatched materials, low tolerance in operating conditions and fuel efficiencies. Enhanced proton conductor shows promise to improve the performances in operating. Higher efficiency of proton conducting solid oxide fuel cell (SOFC—H+) than oxide ion conducting solid oxide fuel cell (SOFC—O2−) can be obtained although its maximum voltage and power density are still lower. The doped BaCeO3 has been found to be one of the best proton conductors but it is unstable in CO2 and H2O containing atmosphere. The conductivity of BaZrO3 is less than BaCeO3 but stable under CO2 and steam atmosphere, particularly 10 mol % Y doped BaZrO3.
The Combination of doped BaCeO3 and BaZrO3 has become motivating due to their high proton conductivity and good stability in humid atmosphere. Several dopants have been studied in order to improve stability and conductivity. In most of the works, some percentage of Ce and/or Zr was substituted by tri-valent cations like Y, Yb, Sc, Pr, Sm etc. at the B-site to make oxygen vacancies to enhance the proton conductivity. Hence, Ce was doped by Zr to increase proton conductivity and chemical stability as investigating on BaCe0.9-xZrxY0.1O2.95 series which show good chemical stability in steam and carbon dioxide atmospheres. Y doping shows potential to enhance conductivity in conventional materials of BaZrO3 and BaCeO3. Y doped BaZrO3 exhibit high conductivity of 7.38 mS/cm at 650° C. Percentage of Ce at B-site has strong effect on proton concentration in perovskite materials.
Sm-doped proton conductors also show promising performance for ITSOFCs. However, very little work has been done to substitute Ba by Sr or Ca which can also have good effect on protonic conductivity.
U.S. Pat. No. 5,387,330 describes a proton conducting oxides BaCe1−xMxO3, where M is a metal dopant, have high proton conductivity at elevated temperatures. Likewise, U.S. Pat. Nos. 6,235,417 and 6,296,687 also disclose electrode materials for SOFCs. U.S. Pat. Nos. 7,842,200, 7,413,678, and 8,012,380 are relevant to the present invention which relates the development of proton conducting electrolytes.
There exist some other patent i.e. U.S. Pat. No. 8,932,781, US20130143142A1, and US2011195342A2 and non-patent prior art (Kang-Rong Lee (a, b), DOI: 10.1016/j.ijhydene.2013.01.043) which disclose proton conducting electrolyte for intermediate temperature solid oxide fuel cell, and fuel cells. However, none of them discloses a combination of doped BaCeO3 and BaZrO3 by doping Sr, Y, and Sm metals.
In order to overcome the aforementioned problems, significant efforts have been devoted to the development of new proton conducting electrolyte for SOFCs.
The present invention discloses a novel proton conducting electrolyte composition having good protonic conductivity and chemical stability at low temperature.